Larson Commercial insider™ Storm Window

The Commercial insider™ delivers measurable energy savings through interior-mounted storm windows that cut drafts by up to 62% and improve U-factor performance by the same margin. Custom fabricated up to 24 feet in width or height, these aluminum-framed units solve the thermal performance problem without touching historic building exteriors.

For Montana’s extreme temperature swings and historic downtowns, the insider™ represents smart retrofit engineering. The interior mounting preserves original facades while delivering modern energy efficiency — critical when -20°F outdoor temps create condensation battles on single-pane glass.

Energy Performance That Contractors Can Sell

The numbers tell the story. Draft reduction: up to 48% (Clear) / 62% (Low-E) translates directly to comfort complaints solved. U-Factor improvement: up to 50% (Clear) / 62% (Low-E) means heating bills drop measurably. When contractors bid energy retrofits, these aren’t theoretical improvements — they’re documented performance gains that justify the investment.

The product is designed to reduce energy loss by up to 50%, making it particularly valuable for Montana’s heating-dominated climate where windows represent the weakest thermal link in most buildings. The Low-E glass option pushes performance even higher, approaching triple-pane territory without the weight and cost of full window replacement.

Performance Metric	Clear Glass	Low-E Glass
Draft Reduction	Up to 48%	Up to 62%
U-Factor Improvement	Up to 50%	Up to 62%
Energy Loss Reduction	Up to 50%	Higher with Low-E
Noise Reduction	Significant	Significant

Custom Fabrication Handles Any Opening

The insider™ system adapts to real-world conditions. Residential: 10” - 80” Width x 10” - 80” Height (Max 23 sq. ft.) covers standard home windows. But the commercial capability sets this apart — Custom fabricated up to 24 feet in width or height means those massive historic courthouse windows or old bank buildings get the same treatment as residential projects.

Tolerance specifications reflect commercial-grade thinking. Tolerances: +/- 1/8” residential, +/- 3/8” commercial acknowledge that century-old buildings aren’t perfectly square. The system compensates without requiring extensive frame modification.

Glass options scale with opening size:

• 1/8” Clear Glass (Standard for 20-95 UI)
• 3/16” Glass (Standard for 95.125 - 110 UI)
• 3/16” Tempered Glass (Required for 110.125+ UI)

Historic Preservation Without Compromise

Interior mount preserves exterior building appearance — the key advantage for historic districts. Montana’s downtown preservation zones often prohibit exterior modifications. The insider™ sidesteps this entirely by mounting inside the existing window frame. Easy removal for seasonal changes means summer ventilation doesn’t require permanent alterations.

The system works with existing window types rather than demanding replacement. Fits single-hung, double-hung, slider, basement, and fixed windows covers most historic building configurations. Measure opening width and height at three points each (use smallest dimension). Install top mounting channel and two side channels using supplied screws. Insert the thermal window panel into the channels.

The product is designed to be installed from the inside, which prevents weathering and allows for easy removal during warmer months or for cleaning. This interior approach eliminates ladder work on multi-story buildings — a significant safety and cost advantage.

Installation Reality Check

Frame depth requirements matter for bidding accuracy. Frame depth: 5/8” actual (1” recommended) residential fits most home window sills. Commercial installations need more: 1 1/4” to 1 5/8” commercial depth depending on mullion configuration.

Typically one tool (screwdriver/drill) completes installation — no specialized equipment rental. The three-channel mounting system keeps labor costs predictable. But contractors should verify existing window conditions, especially in historic buildings where previous modifications might affect mounting depth.

Bottom Line

The Commercial insider™ storm window earned its place in energy retrofit specifications through documented performance. Frustration expressed in trade forums regarding the discontinuation of the product line in 2022 tells the real story — contractors don’t mourn mediocre products. Alternative brands: Quanta-Panel, MonRay, Allied Window (standard commercial/historical alternatives after Larson discontinuation) now fill the gap, but the insider™ set the benchmark.

For Montana contractors working historic preservation or commercial energy retrofits, understanding the insider™ specifications helps evaluate current alternatives. The combination of interior mounting, custom sizing up to 24 feet, and 62% performance improvements established what’s possible. Any replacement product gets measured against these numbers.

FAQ

What size limitations apply to the Commercial insider™?

Residential: 10” - 80” Width x 10” - 80” Height (Max 23 sq. ft.) covers standard home windows. Commercial: Custom fabricated up to 24 feet in width or height handles large institutional openings.

How much energy savings can clients expect?

Draft reduction: up to 48% (Clear) / 62% (Low-E) and U-Factor improvement: up to 50% (Clear) / 62% (Low-E) deliver measurable performance gains. Energy loss reduction up to 50% translates to real heating bill savings in Montana winters.

What mounting depth is required?

Frame depth: 5/8” actual (1” recommended) residential fits most home installations. 1 1/4” to 1 5/8” commercial depth accommodates larger commercial frames with or without mullions.

Can these be removed seasonally?

Yes. Easy to remove for cleaning or seasonal changes allows summer ventilation without permanent modifications. The product is designed to be installed from the inside, which prevents weathering and allows for easy removal during warmer months.

What window types are compatible?

Fits: Single-hung, Double-hung, Slider, Basement, and Fixed/Picture windows covers most existing window configurations in both residential and commercial buildings.